Lubricity improver for diesel oil

ABSTRACT

A fuel oil composition is comprised of diesel oil and a lubricity additive of the formula (I):  
     R—COO—(AO) n —H  (I)  
     wherein R is an alkyl or alkenyl group having from 5 to 19 carbon atoms, AO is a CH 2 CH 2  or C 3 H 6  group and n is a number of 0.5 to 6, wherein the additive is a liquid at 21° C. and having a narrow homolog distribution. The compounds of formula (I) are particularly useful in diesel oils having low sulfur content.

FIELD OF THE INVENTION

[0001] This invention relates to the use of additives for improving thelubricity of diesel oil, to a low-sulfur diesel oil containing theseadditives and to a process for improving the lubricity of diesel oils.

[0002] In the course of efforts to improve the emission behavior ofdiesel fuels, both the contents of polyaromatic compounds and thecontents of long-chain alkanes in diesel oil have been reduced in recentyears. In addition, attempts have been made to reduce the sulfur contentto very low levels, i.e. to values of at most 0.05% by weight andpreferably 0.03% or lower. As a result of these changes in thecomposition of diesel fuels, problems have arisen in the use ofconventional ester-based lubricity enhancers. Partial precipitations canoften occur to the considerable detriment of fuel quality.

[0003] Accordingly, there is a need for lubricity enhancers which couldalso be used in low-sulfur diesel oils. These additives would beeffective in small quantities and, at the same time, would not losetheir effect, even at low temperatures.

[0004] It has now been found that certain alkoxylated compounds solvethis problem.

[0005] In a first embodiment, the present invention relates to the useof fatty acid alkylene glycol esters which are liquid at 21° C. andwhich correspond to general formula (I):

R—COO—(AO)_(n)—H  (I)

[0006] where R is an alkyl or alkenyl group containing 5 to 19 carbonatoms, AO stands the groups CH₂CH₂ or C₃H₆ and n is a number of 0.5 to6, as an additive for improving the lubricity of diesel oil.

[0007] Esters and alkoxylates thereof are already known from WO 96/23855as additives for improving the lubricity of diesel oils. However, WO96/23855 does not disclose the compounds according to the presentinvention with their low degrees of alkoxylation. The only compoundsactually mentioned are a sorbitan mono-oleate and a glycerolmono-oleate.

[0008] Diesel fuels or diesel oils or simply diesel are low-flammabilitymixtures of liquid hydrocarbons which are used as fuels forconstant-pressure or compression-ignition engines (diesel engines) andwhich consist predominantly of paraffins with contents of olefins,naphthenes and aromatic hydrocarbons. Their composition is variable andis dependent in particular on the production method. Typical productshave densities of 0.83 to 0.88, boiling points in the range from 170 to360° C. and solidus points of 70 to 100° C. Diesel oil is obtained inthe distillation of petroleum from gas oil, during cracking, from thetars obtained in the low-temperature carbonization (or hydrogenation) oflignitic or hard coals and by hydrogenation of the coal extract. Dieseloils for stationary installations and for marine engines are similar incomposition to heavy heating oil; diesel oils for automobiles, buses andtrucks correspond in composition to heating oil. During combustion in adiesel engine, air is drawn into the cylinder, heated to 550-900° C. byhigh compression (compression ratio 14:1 to 25:1), so that a jet ofinjected diesel ignites spontaneously and reaches a combustion pressureof 50 to 80 bar at a combustion temperaturs of 1,500 to 2,200° C., sothat the piston is moved and work is done. The combustion of 1 liter ofdiesel in a diesel engine requires 13 m³ of air; the combustion energyreleased amounts to around 42,000 kJ/kg. A key factor for the usabilityof diesel fuels is their ignition response which is now quantitativelyexpressed by the cetane number. Ignition response is the capacity of amotor fuel to ignite relatively easily or with relative difficulty in anengine operating on the diesel principle. With every fuel, this requiresnot only atomization, pressure and temperature, but also a conditioninginterval (ignition delay) before discernible combustion. Good ignitionresponse of a fuel means favorable starting behavior and quiet runningof the diesel engine by virtue of a short conditioning interval or smallignition delay. With a large ignition delay, the known phenomenon of“knocking” comes audibly into play. The requirements for diesel fuelsare a cetane number of 20 to 40 for slow-running engines and a cetanenumber of >45 for small and fast-running engines. The quality featuresof diesel fuels also include low-temperature behavior which can bedescribed by the cloud point or—nowadays preferably—by the cold filterplugging point (CFPP) which is the temperature at which diesel fuel“sucked” through blocks a filter. Other desirable properties include alow pour point, a low content of incombustible or soot-formingsubstances and a low sulfur content. The additives according to theinvention are particularly suitable for use in low-sulfur diesel oils,i.e. diesel oil with a sulfur content of at most 0.05% by weight andpreferably 0.03% by weight or lower. For Europe, the standards and testsfor diesel fuel are specified in DIN-EN 590 (05/1993).

[0009] The fatty acid alkylene glycols are products of the addition ofethylene oxide (EO) or propylene oxide (PO) or both EO and PO onto fattyacids with the formula RCOOH, in which R¹ is as defined above. Compoundswhich contain only EO (CH₂—CH₂ groups) or only propylene oxide groups(C₃H₆ groups) are preferred, the ethoxylated compounds beingparticularly preferred.

[0010] Typical examples are caproic acid, caprylic acid, 2-ethylhexanoicacid, capric acid, lauric acid, isotridecanoic acid, myristic acid,palmitic acid, palmitoleic acid, stearic acid, isostearic acid, oleicacid, elaidic acid, petroselic acid, linoleic acid, linolenic acid,elaeostearic acid, arachic acid, gadoleic acid, behenic acid and erucicacid and the technical mixtures thereof which are obtained, for example,in the pressure hydrolysis of natural fats and oils, in the reduction ofaldehydes from Roelen's oxo synthesis or as monomer fraction in thedimerization of unsaturated fatty acids. Technical C₁₂₋₁₈ fatty acids,such as coconut oil, palm oil, palm kernel oil or tallow fatty acid forexample, are preferred. Ethoxylated or ethoxylated and propoxylatedfatty acids with a degree of alkoxylation n between 1 and 2 areparticularly preferred. The fatty acids may be just propoxylated fattyacids or ethoxylated and propoxylated fatty acids; the ethoxylated andpropoxylated fatty acids may be both random and block compounds.

[0011] The alkoxylates used in accordance with the invention areethoxylated and/or propoxylated fatty acids which are also known asfatty acid alkylene glycols. They are known compounds and may beobtained by reaction of carboxylic acids with alkylene oxide in thepresence of amines as catalysts, for example in accordance withDE-A-2024050. In this process, however, the low-alkoxylated compoundsare obtained in yields of well below 90% of the theoretical. In thisprocess, the ethoxylation is carried out in the presence ofalkanolamines as catalysts and gives distinctly higher yields.

[0012] However, for the propoxylated fatty acids and for the ethoxylatedand propoxylated fatty acids, WO 99/06518 discloses a process whichgives good yields of more than 90% of the theoretical for thelow-propoxylated and ethoxylated/propoxylated fatty acids. This isachieved by carrying out the propoxylation or propoxylation/ethoxylationof the fatty acids in the presence of alkanolamines. Typical examples ofalkanolamines suitable as basic catalysts are monoethanolamine,diethanolamine and, preferably, triethanolamine. The alkanolamines areused in quantities of typically 0.1 to 5% by weight and preferably 0.5to 3.0% by weight, based on the fatty acids. The propoxylation and/orethoxylation/propoxylation reaction can be carried out in known manner.Normally, the fatty acid and the catalyst are introduced into a stirredautoclave which is freed from traces of water before the reaction byalternate evacuation and purging with nitrogen. The fatty acid is thenreacted with the propylene oxide or with the ethylene oxide/propyleneoxide mixture in a molar ratio of 1:0.5 to 1:1.5 which can be introducedinto the pressure reactor in portions through a siphon after heating.The fatty acids are preferably reacted with 1 to 2 mol propylene oxideor with 1 to 2 mol of the ethylene oxide/propylene oxide mixture. Thereaction may be carried out at temperatures of 80 to 180° C. andpreferably at temperatures in the range from 100 to 120° C. and underautogenous pressures of 1 to 5 and preferably 2 to 3 bar. After the endof the reaction, it is advisable to stir the reaction mixture for acertain time (15 to 90 mins.) at the reaction temperature. The autoclaveis then cooled and vented and, if desired, acids, such as lactic acid orphosphoric acid for eample, are added to the product in order toneutralize the basic catalyst.

[0013] According to the invention, liquid compounds corresponding togeneral formula (I) above may generally be used. Compounds (I) where nis a number of 0.5 to 2.5 and, more particularly, 0.5 to 1.5 arepreferred, the odd numbers being obtained by averaging via the differentdegrees of alkoxylation of the individual compounds. A value of nindicates a proportion of unesterified acids. However, additives (I)where n is 1 or greater are preferred.

[0014] It has also been found that, where alkoxylates of formula (I) areused, particularly good results are obtained when they are so-callednarrow-range alkoxylates. Preferably, more than 90% of a homolog shouldbe present in the compounds of formula (I). Homologs of formula (I)where n=1 are particularly preferred.

[0015] With regard to the choice of compounds of formula (I) suitablefor the purposes of the invention, it is essential for the ester to beliquid at 21° C. (room temperature). Accordingly, compounds of formula(I) based on fatty acid mixtures of sunflower oil, tall oil, soybean oilor rapeseed oil are particularly suitable. In addition, fatty acidscontaining at least one olefinic double bond are also preferablyselected as the fatty acid component. Besides unbranched fatty acids,fatty acids with one or more branches may also be used for theproduction of the additives of formula (I). Additives based on oleicacid (a C₁₈ unsaturated fatty acid) are particularly preferred.Particular mention is made in this regard of the 1-EO-oleic acid ester(in formula (I), n=1, R=C₁₇ unsaturated).

[0016] According to the invention, the additives of formula (I) areadded to the diesel oil in quantities of 10 to 1,000 ppm, preferably inquantities of 10 to 250 ppm and more particularly in quantities of 10 to100 ppm. Preferably, less than 100 ppm of the additive is used. Asmentioned above, the quantity of additive should be kept to a minimum.This is achieved in accordance with the invention.

[0017] Other additives, more particularly cetane number improvers(saltpeter or nitrous ester), corrosion inhibitors, flow enhancers,surfactants (which keep the fuel injectors clean), defoamers andoccasionally smoke reducers are introduced into the diesel as additives.Exhaust gases from diesel fuels contain more nitrogen oxides and 30 to100 times more particles (“soot”) than those from spark ignition fuelsafter catalytic cleaning. Such additives may also be used in combinationwith the additives according to the invention. Preferably, however, noother additives should be used to improve lubricity.

[0018] The present invention also relates to a diesel oil with a sulfurcontent of at most 0.05% by weight which contains additives of formula(I) for improving lubricity, preferably in quantities of 10 to 1,000 ppmand more particularly in quantities of less than 100 ppm. In a preferredembodiment, the diesel oil is free from acylated nitrogen-containingcompounds and from free alcohols, more particularly C₆₋₂₂ fatty alcoholsand derivatives thereof, more particularly alkoxylated derivatives.

[0019] The diesel oil according to the invention should contain lessthan 0.05% by weight of sulfur and should have a distillation point(95%- to ASTM-D86) of at most 350° C. The so-called flash point shouldbe at least 38° C.

1-14. (canceled)
 15. A fuel oil composition comprising diesel oil and alubricity additive of the formula (I): R—COO—(AO)_(n)—H  (I) wherein ris an alkyl or alkenyl group having from 5 to 19 carbon atoms, ao is aCH₂CH₂ or C₃H₆ group and n is a number of 0.5 to 6, wherein the additiveis a liquid at 21° C. and having a narrow homolog distribution.
 16. Thecomposition of claim 15 wherein n is equal to from 0.5 to 2.5.
 17. Thecomposition of claim 16 wherein n is equal to from 0.5 to 1.5.
 18. Thecomposition of claim 15 wherein the compound of formula (I) is theproduct of the process comprising reacting ethylene and/or propyleneoxide and a fatty acid selected from the group consisting of sunfloweroil fatty acid, rapeseed oil fatty acid, tall oil fatty acid and/orsoybean oil fatty acid.
 19. The composition of claim 15 wherein theamount of the compound of formula (I) in the fuel oil composition isfrom 10 to 1,000 ppm.
 20. The composition of claim 19 wherein the amountof the compound of formula (I) in the fuel oil composition is from 10 to250 ppm.
 21. The composition of claim 20 wherein the amount of thecompound of formula (I) in the fuel oil composition is from 10 to 100ppm.
 22. The composition of claim 15 wherein the diesel oil has a sulfurcontent of up to 0.05% by weight.
 23. The composition of claim 15wherein the composition is free from other lubricity additives.
 24. Thecomposition of claim 15 wherein the composition is free from acylatednitrogen-containing compounds.
 25. The composition of claim 15 whereinthe composition is free from a C₆₋₂₂ fatty alcohol and/or a derivativethereof.
 26. The composition of claim 15 wherein the derivative is analkoxylate.
 27. A process for improving the lubricity of diesel addingto diesel fuel up to 1,000 ppm of an additive of claim 15.